BIOCHEMICAL DEMONSTRATION OF HCO3- DEPENDENT AND CL--DEPENDENT ATPASE ACTIVITIES IN THE RECTUM OF LARVAL DRAGONFLIES AND INHIBITION OF RECTAL CHLORIDE UPTAKE BY THIOCYANATE

  • 1 January 1980
    • journal article
    • research article
    • Vol. 20  (3) , 217-227
Abstract
Hydrogencarbonate and chloride activated, ouabain-insensitive ATPase activities are demonstrated in the salt-absorbing rectum of larval dragonflies. Maximal activation is achieved at .apprx. 30 mM HCO3- and 20 mM Cl-, respectively. Stimulation of each anion obeys Michaelis-Menten kinetics. Km values are 4.65 mM for HCO3- and 10.25 mM for Cl-activation. The activating anion of 1 type of ATPase simultaneously exerts an inhibitory effect on the other. Cl- activation is also reduced by Mg-ATP in concentrations above 0.5 mM and by Tris-Hepes buffer exceeding 2.5 mM. Both anion-dependent ATPase activities are enriched in subcellular membraneous fractions of the rectum. Thiocyanate inhibits both activities and causes a significant decrease in rectal uptake of radioactive chloride from hypo-osmotic external solution. In the case of HCO3--dependent ATPase a competitive inhibition of SCN- was found with an inhibitor constant of Ki = 0.5 mM.